Effect Of Rootstock And Scion Interaction On Chilling Tolerance Of Grafted Tomato Seedlings

Recently,there are many researches on the effect of grafting on the stress resistance of plants,but most of them focus on the effect of roots on the resistance of grafted seedlings,while there are relatively few studies on the effects of scion and root-scion interactions on the resistance of grafted seedlings are still relatively less.This experiment had collected 40 line of tomato rootstocks to identify them under low temperature stress.On this basis,we selected two rootstock with different low temperature resistance from lines of rootstock to graft tomato,and researched the effects of root,scion,and their interactions on the physiological responses and transcriptional regulatory networks of grafted tomato seedlings under low temperature stress.The purpose was to clarify the mechanism of rootstock,scion and their potential interaction on chilling tolerance of tomato grafted plants,and to provide a theoretical basis for rational selection of root panicle varieties for tomato grafting cultivation in low temperature season.The chief results are showed as follows:1.There is no significant difference in germination rate,germination index and vigor index at 28?among the different rootstock's seeds,but the difference between the germination correlation indexes at 15?and 20?and their relative values at 28?was significant.There were also significant differences in the chilling index among the seedlings of the different rootstocks under the low temperature at 10?/3??day/night?,and the chilling indexes of the seedlings was significantly correlated with the germination indexes under the low temperature condition,but the correlation coefficient at 20?was higher than that at 15?.The regression model of seedling chilling injury index was established by multiple stepwise regression analysis.The relative germination rate and relative germination index at 20?were selected,and the coefficient of the model was 0.9839?P=0.0000?.Through the clustering analysis of seedling chilling injury index,the rootstocks could be divided into cold tolerant,cold sensitive and intermediate types,including six cold tolerant and five cold sensitive materials.We also did the cluster analysis using the two factors selected by the chilling index regression model,and found that the classification of the thirty-nine of the forty materials was the same as that from the cluster analysis of seedling chilling injury index,and the classification of the remaining one was changed into the cold sensitive type from the intermediate type.So the relative germination rate and relative germination index of the seeds at 20?could be used as convenient indicators identifying tomato chilling tolerance.2.Among these 9 kinds of grafted seedlings,S/S seedlings displayed the highest while R/R seedlings displayed the lowest chilling injury index.Meanwhile,R/R seedlings showed the lowest electrolyte leakage,and the highest content of soluble sugar and proline.While R/RS,RS/R,RS/S,S/RS seedlings were intermediate between R/R and S/S regarding the chilling injury index,electrolyte leakage,soluble sugar and proline content.Results indicated that both rootstock and scion are important for chilling tolerance.Further found that rootstock conferred higher chilling resistance than scion,due to the fact that the chilling tolerance of RS/RS was higher than that of S/RS,but lower than R/RS.Moreover,the chilling tolerance of RS-R were significantly higher than those of RS-S,and the P value of interaction were less than 0.01?or 0.05?.The results showed that rootstock and scion had significant interaction effect on the chilling tolerance of grafted seedlings.3.The results showed that low temperature stress reduced the photosynthesis and light energy utilization efficiency of tomato grafted seedlings.Among these 6 varieties of grafted seedlings,S/S seedlings displayed the lowest while R/R seedlings the highest photosynthetic rate?Pn?.Meanwhile,R/R seedlings show the highest pigment,water content,stomatal conductance?Gs?,stomatal limitation?Ls?and Fv/Fm,?ps II and qP values.While RS/R,S/R,R/S,RS/S seedlings were intermediate between R/R and S/S regarding the pigment,water content,photosynthetic rate?Pn?,stomatal conductance?Gs?,stomatal limitation?Ls?and Fv/Fm,?psII and qP values.Indicating that the photosynthetic assimilatory power and light energy utilization efficiency of grafted seedlings with R as root or scion was significantly higher than that of S.Meanwhile,the contents of NO₃^--N and the activities of nitrate reductase?NR?,glutamine synthetase?GS?and glutamate synthase?GOGAT?were significantly decreased in low temperature stress,While the contents of free amino acids,NH₄⁺-N,fructose,sucrose and the activities of sucrose synthase?SS?and sucrose phosphate synthase?SPS?were significantly increased.However,in addition to NH₄⁺-N content,the contents of NO₃^--N,amino acids,fructose,sucrose and the activities of nitrate reductase?NR?,glutamine synthetase?GS?,glutamate synthase?GOGAT?,sucrose synthase?SS?and sucrose phosphate synthase?SPS?in leaves of RS/R,S/R,R/S,RS/S seedlings was lower than that of R/R,but higher than S/S.The results showed that the carbon and nitrogen enrichment ability of R root or scion was higher than that of S.Moreover,The photosynthesis,light use efficiency and carbon and nitrogen assimilatory power of RS-R were significantly higher than those of RS-S,and the P value of interaction were less than 0.01?or 0.05?.The results showed that rootstock and scion had significant interaction effect on photosynthetic fluorescence characteristics and carbon and nitrogen metabolism of grafted seedlings.4.The results showed that low temperature stress significantly increased hydrogen peroxide and the production rate of superoxide anion in leaves and roots of grafted tomato seedlings.However,the reactive oxygen species levels of the grafted seedlings with R as root were significantly lower than those with S as the root.Although the reactive oxygen species level of the grafted seedlings with R as the scion was also significantly lower than that of the grafted seedlings with S as the scion.However,the decrease or increase of scion was less than that of root system,indicating that rootstock conferred more chilling resistance than scion.Meanwhile,the contents of AsA?DHA?GSH?GSSG?ABA and the activities of SOD?POD?CAT?APX?MDHAR?DHAR?GR were significantly increased in low temperature stress.Moreover,except for DHA and GSSG,grafted seedlings with R as root or R as scion were higher,S was lower and RS was middle,indicating that the anti-oxidation and ABA synthesis ability of R-root or scion grafted seedlings under cold stress was significantly higher than that of S.In addition,the anti-oxidation and ABA synthesis ability of RS-R were significantly higher than those of RS-S,and the P value of interaction were less than 0.01?or 0.05?.The results showed that rootstock and scion had significant interaction effect on the chilling tolerance of grafted seedlings.5.At the low temperature stress of 9 days,compared with SRY,80 genes of SY were up-regulated in SRY and down-regulated in RSY compared with RY and RSY.Compared with RSG,there are 70 genes in RSG that up-regulated expression,and down-regulated expression in SRG compared with RG.Through the GO enrichment analysis,a total of 150differentially expressed genes were divided into 101 functional groups,of which 57 items were significantly enriched in the scion,and 44 items were significantly enriched in the root system.Further analysis by KEGG pathway showed that the differentially expressed genes in scions were highly concentrated in the protein processing in endoplasmic reticulum,plant hormone signal transduction,photosynthesis and glutathione metabolism.The differentially expressed genes in the root system are mainly concentrated in the zeatin biosynthesis,starch and sucrose metabolism and plant hormone signal transduction.It is indicate that that rootstock mainly affects the cold resistance of the grafting seedlings by influence the photosynthetic,oxidation-reduction and phytohormone signal transduction pathway of the scion,whereas the scions mainly influence the cold resistance of the grafting seedlings by influence the sugar metabolism of the rootstock and the signal transduction pathway of the plant hormone signal.